1. Technical Field
This invention relates generally to an apparatus and a method for laminating components to a substrate. More particularly, this invention relates to an apparatus and method for vacuum lamination of a two-sided tape and/or a cushion material to a printing plate.
2. Background Information
Flexography is a well-known process for printing advertising material and other indicia on packaging and related materials. The term flexography applies broadly to printing processes utilizing a relief printing plate produced on a flexible substrate. Flexographic printing plates have an uneven surface because of the relief difference between the print and non-print areas of the plate. The presence of the uneven surface becomes problematic when attempting to adhere the printing plate to a two-sided tape sheet or to a foam cushion material for use in a printing operation.
In order to prepare a printing plate for flexography, a two-sided tape is normally applied to the back, or non-relief, side of the printing plate. The two-sided tape is used to adhere the printing plate to a carrier sheet that is thereafter mounted on the printing cylinder.
There are two existing procedures that are generally used to apply a two-sided tape to the non-relief side of the printing plate. One procedure involves unrolling the two-sided tape onto a table surface, and then manually placing one or more printing plates on the tape. In the other procedure, a two-roll laminating apparatus is used, wherein the tape is applied to the plate as the tape and plate are passed between the rolls of the laminating apparatus.
With the first of these procedures, air generally becomes entrapped between the tape and the plate(s) during the application process, due primarily to the uneven surface that is caused by the relief of the plate. When air is entrapped in this manner, one or more air bubbles are formed between the plate and the tape. The air bubbles must be evacuated prior to the printing operation by manually poking or cutting the tape at the site of the bubble, and thereafter forcing the air out. This activity is very labor intensive, since a technician must continually interrupt the tape application process to evacuate the air bubbles. As a result, the cost of the printing plates increases, and/or the capacity to turn out a large number of plates in a given period of time is reduced. If the air entrapped between the tape and the plate is not evacuated, a high spot may result in the plate at that location. A high spot in a plate can cause printing problems (distorted graphics), as well as premature plate wear. Use of the two-roll laminating apparatus for application of the tape to the plate normally results in the entrapment of less air than the manual process; however, the amount of entrapped air may still be larger than desired. In addition, the amount of air entrapment increases with the lamination process as larger plates are used.
During a printing operation, variations in printing pressure are also known to cause printing problems, such as distorted graphics. In order to minimize the occurrence of such problems, a compressible layer, such as a urethane foam cushion, is sometimes adhered to the printing plate. The use of a compressible layer allows the printing plate to maintain generally uniform thickness in the face of the pressure variations. The cushion is generally applied to the underside of the printing plate in a separate application and is not a component of the printing plate per se. The use of a cushion allows for greater flexing of the printing imaging area during the printing process, and allows the plate to rebound more rapidly to its original thickness so that high quality prints can be made.
There are two procedures that are generally used for applying a foam cushion material to the inside of a flexographic printing plate. Conventional photopolymeric printing plates generally include a dimensionally stable substrate on the back side of the printing plate. The first procedure involves delaminating the dimensionally stable substrate from the sheet photopolymer material prior to the development of the relief surface of the plate, and then exposing the back side of the photopolymer material to UV light to condition the floor of the printing plate. The cushion material is then laminated to the photopolymer material by either the manual method or the two-roll laminator referred to above. Following lamination, the sheet photopolymer printing plate is then exposed with ultraviolet light and chemically processed using normal printing plate production procedures. Normal laminating techniques can be employed in this procedure, since the photopolymer material has not yet been processed to form the relief surface prior to the lamination of the cushion material to the solid surface. However, since the printing plate is thereafter processed and developed with the foam cushion already attached inside the plate, great care must be taken to protect the foam cushion from the chemicals used during the plate development process.
The second procedure involves processing a liquid or sheet photopolymer printing plate using normal production procedures to form the relief surface, except in this instance the printing plate having the relief surface is provided with a removable back substrate sheet instead of the more conventional UV adhesive coated back substrate sheet. The removable back substrate sheet is delaminated from the printing plate, and the cushion material is then adhered to the printing plate. In this procedure normal laminating techniques cannot be used because of the uneven surface resulting from the relief difference between the print and non-print areas of the plate. Air may become entrapped between the cushion material and the printing plate, causing delamination of the two materials, as well as premature wear and distorted graphics.
It is desired to provide an apparatus and method for laminating components to a substrate that is economical and convenient to use, and that avoids the problems of prior art devices.